The Living Barrier: A Primer on Transfer across Biological Membranes provides information pertinent to the movement of molecules across cell membranes. This book covers a variety of topics, including cell membrane, membrane transfer, water transfer, and movement of charged solutes. Organized into nine chapters, this book begins with an overview of the basic ideas of the cell membrane and reviews the experimental evidence about the structure of the cell membrane. This text then reviews the classical electron microscope pictures of membranes. Other chapters consider the interactions between electrical potentials and the movements of charged substances, which make the membrane transfer of these substances much more complicated than those of neutral molecules. This book discusses as well the aspects of water structure and its influence on membrane permeability. The final chapter deals with the methods by which membranes are synthesized. This book is a valuable resource for biochemists, physiologists, pharmacologists, and botanists.

The overall goal of this project was to develop reactive membrane barriers--a new and flexible technique to contain and stabilize subsurface contaminants. Polymer membranes will leak once a contaminant is able to diffuse through the membrane. By incorporating a reactive material in the polymer, however, the contaminant is degraded or immobilized within the membrane. These processes increase the time for contaminants to breakthrough the barrier (i.e. the lag time) and can dramatically extend barrier lifetimes. In this work, reactive barrier membranes containing zero-valent iron (Fe°) or crystalline silicotitanate (CST) were developed to prevent the migration of chlorinated solvents and cesium-137, respectively. These studies were complemented by the development of models quantifying the leakage/kill time of reactive membranes and describing the behavior of products produced via the reactions within the membranes. First, poly(vinyl alcohol) (PVA) membranes containing Fe° and CST were prepared and tested. Although PVA is not useful in practical applications, it allows experiments to be performed rapidly and the results to be compared to theory. For copper ions (Cu{sup 2+}) and carbon tetrachloride, the barrier was effective, increasing the time to breakthrough over 300 times. Even better performance was expected, and the percentage of the iron used in the reaction with the contaminants was determined. For cesium, the CST laden membranes increased lag times more than 30 times, and performed better than theoretical predictions. A modified theory was developed for ion exchangers in reactive membranes to explain this result. With the PVA membranes, the effect of a groundwater matrix on barrier performance was tested. Using Hanford groundwater, the performance of Fe° barriers decreased compared to solutions containing a pH buffer and high levels of chloride (both of which promote iron reactivity). For the CST bearing membrane, performance improved by a factor of three when groundwater was used in place of deionized water. The performance of high density polyethylene (HDPE) membranes containing Fe° was then evaluating using carbon tetrachloride as the target contaminant. Only with a hydrophilic additive (glycerol), was the iron able to extend lag times. Lag times were increased by a factor of 15, but only 2-3% of the iron was used, likely due to formation of oxide precipitates on the iron surface, which slowed the reaction. With thicker membranes and lower carbon tetrachloride concentrations, it is expected that performance will improve. Previous models for reactive membranes were also extended. The lag time is a measurement of when the barrier is breached, but contaminants do slowly leak through prior to the lag time. Thus, two parameters, the leakage and the kill time, were developed to determine when a certain amount of pollutant has escaped (the kill time) or when a given exposure (concentration x time) occurs (the leakage). Finally, a model was developed to explain the behavior of mobile reaction products in reactive barrier membranes. Although the goal of the technology is to avoid such products, it is important to be able to predict how these products will behave. Interestingly, calculations show that for any mobile reaction products, one half of the mass will diffuse into the containment area and one half will escape, assuming that the volumes of the containment area and the surrounding environment are much larger than the barrier membrane. These parameters/models will aid in the effective design of barrier membranes.

The plan of this book is to present the relevant thermodynamic features of fluid mixtures in contact with semipermeable barriers, then to apply this information in deriving the design requirements of individual membrane separation processes. The membranes, by this approach, are introduced by way of the mass transport and selectivity demands which they are to meet. This book gives a survey, in systematic order, of the terms and concepts by which barrier separations operate.

Buildings are often constructed on sites where volatile organic compounds (VOCs) such as benzene, toluene, chlorinated solvents, ethers etc. are in the ground. The usual remedial solution is to provide a gas membrane under or over the floor slab, of the same type as used to prevent methane and carbon dioxide migration into buildings. This guide provides a summary of the functions of a vapour membrane and the factors that may affect the performance of the membrane in a protection system for a building on land contaminated by VOCs.